linux-kernel - Re: [PATCH] tracing/user_events: Run BPF program if attached

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Date:   Tue, 9 May 2023 08:24:29 -0700
From:   Alexei Starovoitov <alexei.starovoitov@...il.com>
To:     Beau Belgrave <beaub@...ux.microsoft.com>
Cc:     Steven Rostedt <rostedt@...dmis.org>,
        Masami Hiramatsu <mhiramat@...nel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        linux-trace-kernel@...r.kernel.org,
        Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Andrii Nakryiko <andrii@...nel.org>, bpf <bpf@...r.kernel.org>
Subject: Re: [PATCH] tracing/user_events: Run BPF program if attached

On Mon, May 8, 2023 at 9:38 AM Beau Belgrave <beaub@...ux.microsoft.com> wrote:
>
> Programs that utilize user_events today only get the event payloads via
> perf or ftrace when writing event data. When BPF programs are attached
> to tracepoints created by user_events the BPF programs do not get run
> even though the attach succeeds. This causes confusion by the users of
> the programs, as they expect the data to be available via BPF programs
> they write. We have several projects that have hit this and requested
> BPF program support when publishing data via user_events from their
> user processes in production.
>
> Swap out perf_trace_buf_submit() for perf_trace_run_bpf_submit() to
> ensure BPF programs that are attached are run in addition to writing to
> perf or ftrace buffers. This requires no changes to the BPF infrastructure
> and only utilizes the GPL exported function that modules and other
> components may use for the same purpose. This keeps user_events consistent
> with how other kernel, modules, and probes expose tracepoint data to allow
> attachment of a BPF program.

Sorry, I have to keep my Nack here.

I see no practical use case for bpf progs to be connected to user events.

There must be a different way to solve your user needs
and this is not bpf.